Honeycomb structure and catalyst for cleaning exhaust gas using same, and method for producing catalyst for cleaning exhaust gas

ABSTRACT

The present invention addresses the problem and purpose of providing a honeycomb structure that has a sufficiently high strength and is excellent in endurance, and a catalyst for cleaning an exhaust gas using the same that is excellent in resistance to sulfur oxide (SOX). The honeycomb structure of the present invention is one consists of a flat inorganic fiber sheet comprising an inorganic fiber sheet having supported thereon an inorganic binder and zeolite, and a corrugated inorganic fiber sheet comprising an inorganic fiber sheet having supported thereon the same inorganic binder and zeolite, which are alternately combined with each other, wherein it is characterized in that the zeolite has a particle diameter (i.e., a median particle diameter, D50) of from 0.5 to 10.0 μm.

TECHNICAL FIELD

The present invention relates to a honeycomb structure, which are used,for example, in a cleaning method for removing a nitrogen oxide (NOx)from a combustion exhaust gas, a catalyst for cleaning an exhaust gasusing the same, and a method for producing a catalyst for cleaning anexhaust gas.

BACKGROUND ART

For example, an exhaust gas discharged from a marine vessel engine has ahigh sulfur oxide (SOx) concentration and a high nitrogen oxide (NOx)concentration in the exhaust gas due to the use of a C fuel as a fuel,and ammonia (NH₃) or the like used as a reducing agent for a denitrationreaction is reacted with a sulfur oxide (SOx) to form ammonium sulfate.The exhaust gas from the marine vessel engine has a temperature of 300°C. or less, and generally approximately 250° C., and under thecondition, ammonium sulfate is generated in the exhaust gas to fail toretain the stable catalyst capability.

Patent Literature 1 below discloses an exhaust gas cleaning method usinga catalyst having a denitration capability removing a nitrogen oxide(NOx) even in an exhaust gas containing a sulfur oxide, and describes anexhaust gas cleaning method for reducing and removing a nitrogen oxideNOx in an exhaust gas in such a manner that β-zeolite having supportedthereon iron, cobalt, silver, molybdenum, or tungsten is used as thedenitration catalyst, and an oxygen excessive exhaust gas is made incontact therewith in the presence of ethanol and/or isopropyl alcohol asa reducing agent.

Patent Literature 2 below describes an exhaust gas cleaning method forreducing and removing a nitrogen oxide NOx in an exhaust gas in such amanner that proton-type β-zeolite is used as a catalyst, and an oxygenexcessive exhaust gas is made in contact therewith in the presence ofethanol and/or isopropyl alcohol as a reducing agent.

Patent Literature 3 below describes an exhaust gas cleaning method usingZSM-5 type zeolite having supported thereon cobalt, which is produced insuch a manner that Na-ZSM-5 type zeolite or H-ZSM-5 type zeolite havingan SiO₂/Al₂O₃ ratio of 27 or more and 100 or less is used as a catalystsupport, and the catalyst support is immersed in an aqueous solution ofcobalt salt (such as nitrate, acetate, or chloride of cobalt) to performion exchange between the Na (or H) present on the catalyst support andCo at an ion exchange rate of from 40 to 100%, as a denitrationcatalyst, and a liquefied petroleum gas containing propane and butane inthe composition thereof as a reducing agent.

However, the exhaust gas cleaning methods by the reduction and removingusing the denitration catalyst described in Patent Literatures 1 to 3have a problem that the reaction temperature of the exhaust gas cleaningis approximately from 300 to 500° C., which is higher than thetemperature of the exhaust gas from the marine vessel engine.

Under the circumstances, the present applicant have proposed in PatentLiterature 4 below a method for cleaning a combustion exhaust gas thatis capable of effectively decreasing a nitrogen oxide from a combustionexhaust gas discharged, for example, from a marine vessel engine, havinga high concentration of a nitrogen oxide (NOx) and a sulfur oxide (SOx)present therein, and having a low exhaust gas temperature of 300° C. orless.

In the method for cleaning a combustion exhaust gas disclosed in PatentLiterature 4, a substrate for producing a honeycomb structure isproduced by performing a step of coating a slurry formed of zeolite,water, and a silica sol on a glass fiber sheet, and then a honeycombstructure is produced by performing a step of corrugating the sodiumtype zeolite-supported substrate to provide a corrugated glass fibersheet substrate, a step of processing the substrate to a flat glassfiber sheet to provide a flat glass fiber sheet substrate, and a step oflaminating the corrugated glass fiber sheet substrate and the flat glassfiber sheet substrate alternately. The zeolite-supported honeycombstructure produced by the aforementioned method is subjected to a stepof performing ion exchange with a catalyst metal, so as to produce ahoneycomb denitration catalyst.

Patent Literature 1: JP-A-2004-358454

Patent Literature 2: JP-A-2004-261754

Patent Literature 3: JP-A-11-188238

Patent Literature 4: JP-A-2013-226545

DISCLOSURE OF INVENTION Technical Problem

However, the method described in Patent Literature 4 has a problem thatthe property of the zeolite that is easily solidified is unclear in thecase where the zeolite-containing slurry is coated on the glass fibersheet, and it is difficult to produce a honeycomb structure that has asufficiently high strength and is excellent in endurance property.

Furthermore, there is a problem that it is difficult to produce adenitration catalyst that is excellent in resistance to a sulfur oxide(SOx).

An object of the present invention is to solve the problems in the priorart described above, and to provide a honeycomb structure that has asufficiently high strength and is excellent in endurance property, and acatalyst for cleaning an exhaust gas using the same that is excellent inresistance to a sulfur oxide (SOx).

Solution to Problem

As a result of earnest investigations accumulated by the inventors, ithas been found that in the production of a honeycomb structure bycoating a zeolite-containing slurry on an inorganic fiber sheet, zeolitehaving a large particle diameter is not flocculated to fail to produce ahoneycomb structure having a high strength, and as for the zeoliteproperties (particle diameter) in the production of a honeycombstructure, the use of zeolite having a prescribed particle diameterenables the production of a honeycomb structure having a sufficientstrength, and thus the present invention has been completed.

For achieving the aforementioned objects, the invention of a honeycombstructure of claim 1 is a honeycomb structure consisting of a flatinorganic fiber sheet comprising an inorganic fiber sheet havingsupported thereon an inorganic binder and zeolite, and a corrugatedinorganic fiber sheet comprising an inorganic fiber sheet havingsupported thereon the same inorganic binder and zeolite, which arealternately combined with each other, wherein it is characterized inthat the zeolite has a particle diameter (i.e., a median particlediameter, D50) of from 0.5 to 10.0 μm.

The particle diameter of the zeolite herein means a particle diametercorresponding to 50% in the volume-based cumulative particle sizedistribution (i.e., a median particle diameter, D50) measured by a laserdiffraction method. The measurement of sample is performed afterdispersing in water. At this time, for making a state where theparticles are sufficiently dispersed in water, the particles aredispersed with an ultrasonic homogenizer, and the measurement result isrecorded after confirming that the results of the particle diameterdistribution is not fluctuated.

In the honeycomb structure described above, the inorganic fiber sheet ispreferably a glass fiber sheet.

In the honeycomb structure described above, the inorganic binder ispreferably formed of zirconia, alumina, silica, silica-alumina, ortitania, and the inorganic binder is particularly preferably formed ofzirconia or alumina.

The invention of claim 3 is a catalyst for cleaning an exhaust gas usinga honeycomb structure, wherein it is characterized in that it contains adenitration catalyst component that is supported on the zeolite of theaforementioned honeycomb structure.

In the catalyst for cleaning an exhaust gas using the honeycombstructure described above, the inorganic binder is preferably formed ofzirconia or alumina.

In the catalyst for cleaning an exhaust gas using a honeycomb structure,the denitration catalyst component is preferably bismuth.

The present invention also relates to a method for producing thecatalyst for cleaning an exhaust gas having bismuth as the denitrationcatalyst component described above, wherein it is characterized in thatthe method comprises a step of supporting bismuth (Bi) on the zeolite,in the step, bismuth (Bi) being dissolved in a solvent, the solvent usedbeing a compound having one or more alkoxy group and one or more hydroxygroup per molecule, a compound having two or more hydroxy groups permolecule, or an acid.

The present invention also relates to a method for producing a catalystfor cleaning an exhaust gas comprising an inorganic fiber sheet havingsupported thereon an inorganic binder and zeolite, in which the methodcomprises a step of supporting bismuth (Bi) as a denitration catalystcomponent on the zeolite, in the step, bismuth (Bi) being dissolved in asolvent, the solvent used being a compound having one or more alkoxygroup and one or more hydroxy group per molecule, a compound having twoor more hydroxy groups per molecule, or an acid.

Advantageous Effects of Invention

According to the present invention, such an effect is provided that theuse of the zeolite having the prescribed particle diameter describedabove provides a honeycomb structure that has a sufficiently highstrength, ensures the use in a state with high endurance propertyagainst the external factors, such as vibration, and is excellent indurability.

Such an effect is also provided that the use of the honeycomb structurethat has a sufficiently high strength, ensures the use in a state withhigh endurance property against the external factors, such as vibration,and is excellent in durability enhances the durability of a catalyst forcleaning an exhaust gas.

Furthermore, the increase of the amount of bismuth in the form of ion inthe solvent increases the amount thereof that is ion-exchanged in thezeolite, and thereby bismuth is uniformly supported on the zeolite. As aresult, a compound formed by bonding to SOx is prevented from beingformed, and thereby the SOx durability is enhanced.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a flow chart showing one example of a denitration ratemeasuring instrument used in the catalyst capability test in the exampleof the present invention.

DESCRIPTION OF EMBODIMENT

Embodiments of the present invention will be described in detail below.

The honeycomb structure according to the present invention consists of aflat inorganic fiber sheet comprising an inorganic fiber sheet havingsupported thereon an inorganic binder and zeolite, and a corrugatedinorganic fiber sheet comprising an inorganic fiber sheet havingsupported thereon the same inorganic binder and zeolite, which arealternately combined with each other, wherein it is characterized inthat the zeolite has a particle diameter (i.e., a median particlediameter, D50) of from 0.5 to 10.0 μm, and preferably from 3.0 to 7.0μm.

The particle diameter of the zeolite herein means a particle diametercorresponding to 50% in the volume-based cumulative particle sizedistribution (i.e., a median particle diameter, D50) measured by a laserdiffraction method.

In the present invention, zeolite particles having a particle diameter(D50) of from 0.5 to 10.0 μm are used for ensuring the strength of thehoneycomb structure. In the case where the zeolite particles have alarge particle diameter exceeding the range described above, thecontacts between the zeolite particles and the inorganic binders aredecreased to make difficult the form retention. Zeolite particles havinga small particle diameter that is less than the range described aboveare not practical due to the complexity in industrial production. Theuse of the zeolite particles having a particle diameter within the rangedescribed above increases the contacts to the inorganic binders, so asto ensure the strength suitable for the form retention.

The flat inorganic fiber sheet comprising an inorganic fiber sheethaving supported thereon an inorganic binder and the zeolite, and thecorrugated inorganic fiber sheet comprising an inorganic fiber sheethaving supported thereon the same inorganic binder and the zeolite arealternately combined with each other, so as to produce a honeycombstructure.

For achieving the prescribed particle diameter (i.e., the medianparticle diameter, D50) of the zeolite, commercially available zeolitemay be used after pulverizing.

In the present invention, the honeycomb structure means an integratedstructure consisting of plural through holes (cells) partitioned with apartitioning wall, through which an exhaust gas is capable of passing,and the partitioning wall, and the cross sectional shape of the throughholes described above (i.e., the cross sectional shape of the cells) isnot particularly limited, examples of which include a circular shape, acircular arc shape, a square shape, a rectangular shape, and a hexagonalshape.

In the honeycomb structure described above, the inorganic fiber sheet ispreferably a glass fiber sheet or a ceramic fiber sheet.

In the honeycomb structure described above, the inorganic binder ispreferably formed of zirconia, alumina, silica, silica-alumina, ortitania, and the inorganic binder is particularly preferably formed ofzirconia or alumina.

Another denitration catalyst according to the present invention may be acatalyst for cleaning an exhaust gas (denitration catalyst) formed ofsmall pieces of the substrate of the honeycomb structure (i.e., thoseformed only of the flat substrate or the corrugated substrate) or thosein a pellet form.

When the small pieces of the substrate of the honeycomb structure have acorrugated form having one or more repeating concave grooves, they havesmall values for each of the width dimension per one of the concavegroove (denoted by A), the repetition number in the width direction(denoted by n), the height dimension (denoted by B), and the depthdimension (denoted by C).

In the small pieces of the substrate of the honeycomb structure, thewidth dimension (A) is 2.0 mm or more, preferably 3.0 mm or more, andmore preferably 4.0 mm or more. The width dimension (A) is preferably100 mm or less, more preferably 50 mm or less, further preferably 25 mmor less, and still further preferably 10 mm or less.

The height dimension (B) is 1.0 mm or more, preferably 2.0 mm or more,and more preferably 3.0 mm or more. The height dimension (B) ispreferably 50 mm or less, more preferably 25 mm or less, and furtherpreferably 10 mm or less. The repetition number in the width direction(n) is from 1 to 100, preferably from 1 to 10, more preferably from 1 to5, and further preferably from 2 to 4.

The depth dimension (C) is 3.0 mm or more, preferably 4.0 mm or more,and more preferably 5.0 mm or more. The depth dimension (C) ispreferably 200 mm or less, more preferably 100 mm or less, furtherpreferably 50.0 mm or less, still further preferably 20.0 mm or less,still further preferably 15.0 mm or less, and still further preferably10.0 mm or less.

Preparation of Honeycomb Structure Preparation of Substrate

The zeolite having the particular particle diameter described above, asolvent, and the inorganic binder are mixed to prepare a slurry. Theslurry is coated on glass fiber paper as the inorganic fiber sheet.

The zeolite is preferably MFI zeolite or FER zeolite, and the zeoliteused may also be MOR zeolite, BEA zeolite, or the like.

The inorganic binder used may be silica, titania, alumina,silica-alumina, zirconia, or the like.

In the case where silica is used as the inorganic binder, a silica solused may be an acidic type containing approximately 20% by weight ofsilica (while neutral and basic types may also be used). The weightratio of the zeolite, water, and silica sol as the inorganic binder maybe controlled, for example, to 100/75/46.

Subsequently, the slurry described above is coated on a glass fibersheet. Any known coating method may be used for coating, and examplesthereof include a so-called dipping method, a brush coating method, aspray coating method, and a drop coating method.

Shaping of Substrate

The slurry-coated glass fiber sheet is then shaped with a corrugatingmold and a pressing jig, the corrugated slurry-coated glass fiber sheetthus shaped is dried under condition of from 100 to 200° C. for from 1to 2 hours and released from the mold, and separately the flatslurry-coated glass fiber sheet having not been shaped is dried undercondition of from 100 to 200° C. for from 1 to 2 hours. At this time,the inorganic binder, such as a silica sol, added to the slurryfunctions as a binder between the glass fiber sheet and the zeolite, soas to enable retention of the corrugated form after shaping the glassfiber sheet.

The corrugated slurry-coated glass fiber sheet and the flatslurry-coated glass fiber sheet are calcined under condition of from 300to 550° C. for from 1 to 4 hours.

The corrugated glass fiber sheet substrate and the flat glass fibersheet substrate thus obtained are then laminated alternately to providethe honeycomb structure.

The honeycomb structure according to the present invention consists of aflat glass fiber sheet comprising an inorganic fiber sheet havingsupported thereon an inorganic binder and zeolite, and a corrugatedglass fiber sheet comprising an inorganic fiber sheet having supportedthereon the same inorganic binder and zeolite, which are alternatelycombined with each other, wherein it is characterized in that thezeolite has a particle diameter (i.e., a median particle diameter, D50)of from 0.5 to 10.0 μm. According to the present invention, the use ofthe zeolite having the particular particle diameter described above canprovide a honeycomb structure that has a sufficiently high strength,ensures the use in a state with high endurance property against theexternal factors, such as vibration, and is excellent in durability.

The catalyst for cleaning an exhaust gas according to the presentinvention is characterized in that it contains a denitration catalystcomponent that is supported on the zeolite of the aforementionedhoneycomb structure.

In the catalyst for cleaning an exhaust gas using the aforementionedhoneycomb structure, the inorganic binder is preferably zirconia oralumina.

The catalyst for cleaning an exhaust gas preferably contains, as thedenitration catalyst component, a metallic element consisting of bismuth(Bi) on the zeolite.

The precursor compound of the metallic element to be supported may be aninorganic acid salt (such as nitrate and chloride) or an organic acidsalt (such as acetate). Any supporting method for the catalyst metal maybe used as far as the denitration capability is exhibited, and examplesthereof include an ion exchange method and an impregnation supportingmethod. Examples of the ion exchange method include such a method thatzeolite is suspended in an aqueous solution containing a precursorcompound of bismuth (Bi), and the zeolite having the catalyst metalbonded thereto through ion exchange is taken out from the aqueoussolution, dried, and then calcined.

In the case where a metallic element consisting of bismuth (Bi) is to besupported as the denitration catalyst component on the zeolite, theprecursor compound of the metallic element to be supported may be aninorganic acid salt (such as nitrate and chloride), an organic acid salt(such as acetate), or an oxide. Any supporting method for the catalystmetal may be used as far as the denitration capability is exhibited, andexamples thereof include an ion exchange method and an impregnationsupporting method. Examples of the ion exchange method include such amethod that zeolite having the catalyst metal bonded thereto through ionexchange is taken out from the solvent, dried, and then calcined.

Examples of the solvent for dissolving the aforementioned precursorcompound of bismuth include a compound having one or more alkoxy groupand one or more hydroxy group per molecule, and a compound having two ormore hydroxy groups per molecule, and an acid.

The compound having one or more alkoxy group and one or more hydroxygroup per molecule used is preferably 2-methoxyethanol. The compoundhaving two or more hydroxy groups per molecule used is preferablyethylene glycol. The acid used is preferably nitric acid or acetic acid.

In the denitration catalyst according to the present invention, acompound having one or more alkoxy group and one or more hydroxy groupper molecule, a compound having two or more hydroxy groups per molecule,such as a diol compound, or an acid is used as the solvent, and thus ithas such a feature that bismuth is present in the form of ion in thecatalyst slurry. According to the present invention, bismuth isuniformly supported on the zeolite.

According to the catalyst for cleaning an exhaust gas using thehoneycomb structure of the present invention, the use of the zeolitehaving the particular particle diameter described above can provide thecatalyst for cleaning an exhaust gas using the honeycomb structure thathas a sufficiently high strength, ensures the use in a state with highendurance property against the external factors, such as vibration, andis excellent in durability.

According to the catalyst for cleaning an exhaust gas of the presentinvention having zirconia or alumina as the inorganic binder, inparticular, a nitrogen oxide can be effectively decreased from acombustion exhaust gas having a high concentration of a nitrogen oxide(NOx) and a sulfur oxide (SOx) present therein, and having a low exhaustgas temperature of 300° C. or less, discharged, for example, from amarine vessel engine, i.e., a large marine vessel diesel engine, a largescale boiler for a factory, an electric power plant, a community centralheating and air-conditioning plant, and the like.

In the case where the aforementioned bismuth compound is supported onthe zeolite, while the step of supporting may be performed as a separatestep after producing the honeycomb structure from glass paper, the stepof supporting may be performed in the course of from the glass paper tothe honeycomb structure, or may be performed simultaneously with thepreparation of the substrate of the honeycomb structure by mixing theaforementioned bismuth solution with the slurry formed of the zeolite,the solvent, and the inorganic binder.

In the catalyst for cleaning a combustion exhaust gas according to thepresent invention, the reducing agent is not particularly limited as faras it has a reducing power at the temperature where the combustionexhaust gas is reduced, and methanol or ethanol, as an alcohol having asmall number of carbon, is preferably used.

EXAMPLE

Examples of the present invention will be described below withcomparative examples, but the present invention is not limited to theexamples.

Example 1

FER zeolite having a particle diameter (D50) of 7.0 μm (CP914C, a tradename, produced by Zeolyst International) was used, and 25 g of thezeolite, 18.75 g of ion exchanged water, and 11.5 g of an aqueoussolution of a silica sol (solid concentration: 22.0% by weight) as aninorganic binder were mixed to provide a slurry. 18 g of the slurry wascoated on glass paper of 100 mm×150 mm to provide flat slurry-coatedglass paper, and then the flat slurry-coated glass paper was dried at110° C. for 1 hour. Separately, 27.6 g of the slurry described above wascoated on glass paper of 100 mm×230 mm, the slurry-coated glass paperwas shaped with a corrugating mold and a pressing jig, the corrugatedslurry-coated glass paper thus shaped is dried at 110° C. for 1 hour,and released from the mold. Thereafter, the flat slurry-coated glasspaper and the corrugated slurry-coated glass paper were calcined at atemperature of 500° C. for 3 hours. Two plies of the flat silicasol-zeolite-supported glass paper and one ply of the corrugated silicasol-zeolite-supported glass paper were combined alternately, therebyproducing a honeycomb structure.

The particle diameter of the zeolite herein is a particle diametercorresponding to 50% in the volume-based cumulative particle sizedistribution (i.e., a median particle diameter, D50) measured by a laserdiffraction method, and the particle diameter (D50) of the zeolite wasmeasured with a laser diffraction and scattering particle size analyzer(Microtrac MT3300EXII, a trade name, produced by Nikkiso Co., Ltd.).

Example 2

A honeycomb structure according to the present invention was produced inthe same manner as in Example 1 described above provided that thedifference from Example 1 described above was that FER zeolite having aparticle diameter (D50) of 3.0 μm was used.

Example 3

A honeycomb structure according to the present invention was produced inthe same manner as in Example 1 described above provided that thedifference from Example 1 described above was that MFI zeolite having aparticle diameter (D50) of 6.0 μm was used.

Comparative Example 1

For comparison, a honeycomb structure was produced in the same manner asin Example 1 described above provided that the difference from Example 1described above was that FER zeolite having a particle diameter (D50) of36.0 μm was used.

Comparative Example 2

For comparison, a honeycomb structure was produced in the same manner asin Example 1 described above provided that the difference from Example 1described above was that FER zeolite having a particle diameter (D50) of14.0 μm was used.

Evaluation of Strength

The honeycomb structures obtained in Examples 1 to 3 according to thepresent invention and Comparative Examples 1 and 2 were evaluated byvisually observing for the strength of the honeycomb structures, and theresults obtained are shown in Table 1 below. The evaluation standard isas follows.

Observation of Strength of Honeycomb Structure

A: The silica sol-zeolite-supported glass paper can be corrugated, andin the production of the honeycomb structure by combining alternatelythe corrugated silica sol-zeolite-supported glass paper and the flatsilica sol-zeolite-supported glass paper, the corrugated form of thecorrugated silica sol-zeolite-supported glass paper is not broken toretain the strength.

B: The silica sol-zeolite-supported glass paper can be corrugated, butin the production of the honeycomb structure by combining alternatelythe corrugated silica sol-zeolite-supported glass paper and the flatsilica sol-zeolite-supported glass paper, the corrugated form of thecorrugated silica sol-zeolite-supported glass paper cannot be retainedto break the honeycomb structure.

C: The silica sol-zeolite-supported glass paper cannot be corrugated,and no honeycomb structure can be produced.

TABLE 1 Strength of Particle diameter (D50) honeycomb (μm) structureExample 1 7 A Example 2 3 A Example 3 6 A Comparative Example 1 36 CComparative Example 2 14 B

As apparent from the results shown in Table 1 described above, accordingto the honeycomb structures of Examples 1 to 3 according to the presentinvention, a honeycomb structure that has a sufficiently high strength,ensures the use in a state with high endurance property against theexternal factors, such as vibration, and is excellent in durability canbe obtained by using zeolite having the particular particle diameter. InComparative Examples 1 and 2, on the other hand, it is understood thatdue to the large particle diameters (D50) of the zeolite exceeding therange of from 0.5 to 10.0 μm, the contacts between the zeolite particlesand the inorganic binder are decreased, and thus in the production ofthe honeycomb structure by alternately combining the corrugated silicasol-zeolite-supported glass paper and the flat silicasol-zeolite-supported glass paper, the form of the corrugated silicasol-zeolite-supported glass paper is not retained, resulting in breakageof the honeycomb structure, or the silica sol-zeolite-supported glasspaper cannot be corrugated, resulting in failure in production of thehoneycomb structure.

Example 4

A denitration catalyst for cleaning an exhaust gas using a honeycombstructure according to the present invention was produced in thefollowing manner.

FER zeolite having a particle diameter (D50) of 7.0 μm (CP914C, a tradename, produced by Zeolyst International) was used, and 20 g of thezeolite, 9.2 g of a zirconia sol (Zircosol 20A, a trade name, producedby Daiichi Kigenso Kagaku Kogyo Co., Ltd.) as an inorganic binder, 2.65g of bismuth nitrate (Bismuth(III) Nitrate Pentahydrate, a trade name,produced by Kishida Chemical Co., Ltd.), and 20 g of ion exchanged waterwere mixed and agitated at room temperature for 1 hour to provide aslurry having a solid concentration of 46.8% by weight. The slurry wascoated on glass paper of 100 mm×150 mm to provide flat slurry-coatedglass paper, and then the flat slurry-coated glass paper was dried at110° C. for 1 hour. Separately, the slurry described above was coated onglass paper of 100 mm×230 mm, the slurry-coated glass paper was shapedwith a corrugating mold and a pressing jig, the corrugated slurry-coatedglass paper thus shaped is dried at 110° C. for 1 hour, and releasedfrom the mold. Thereafter, the flat slurry-coated glass paper and thecorrugated slurry-coated glass paper were calcined at a temperature of500° C. for 3 hours, thereby providing flat glass paper having supportedthereon the zeolite, bismuth (Bi) as the denitration catalyst metal, andthe zirconium compound as the shape maintaining binder, and corrugatedglass paper having supported thereon the same materials. Two plies ofthe flat catalyst-supported glass paper and one ply of the corrugatedcatalyst-supported glass paper were combined alternately, therebyproducing a denitration catalyst for cleaning a combustion exhaust gasusing the honeycomb structure.

Example 5

A denitration catalyst for cleaning a combustion exhaust gas using ahoneycomb structure according to the present invention was produced inthe same manner as in Example 4 described above provided that thedifference from Example 4 described above was that an aqueous solutioncontaining an alumina sol (Aluminasol 520, a trade name, produced byNissan Chemical Industries, Ltd.) as the inorganic binder was usedinstead of the zirconia sol (Zircosol 20A) as the inorganic binder.

Reference Example 1

A denitration catalyst for cleaning a combustion exhaust gas using ahoneycomb structure according to the present invention was produced inthe same manner as in Example 4 described above provided that thedifference from Example 4 described above was that an aqueous solutioncontaining a silica sol (Silicadol 20A, a trade name, produced by NipponChemical Industrial Co., Ltd.) as the inorganic binder was used insteadof the zirconia sol (Zircosol 20A) as the inorganic binder.

Reference Example 2

A denitration catalyst for cleaning a combustion exhaust gas using ahoneycomb structure according to the present invention was produced inthe same manner as in Example 4 described above provided that thedifference from Example 4 described above was that an aqueous solutioncontaining a titania sol (Titaniasol S-300A, a trade name, produced byMillennium Inorganic Chemicals, Inc.) as the inorganic binder was usedinstead of the zirconia sol (Zircosol 20A) as the inorganic binder.

Evaluation of Strength

The honeycomb structures obtained in Examples 4 and 5 according to thepresent invention and Reference Examples 1 and 2 were evaluated byvisually observing for the strength of the honeycomb structures based onthe aforementioned evaluation standard, and the results obtained areshown in Table 4 below.

Evaluation of Denitration Capability

The denitration catalysts for cleaning a combustion exhaust gas usingthe honeycomb structures obtained in Examples 4 and 5 according to thepresent invention and Reference Examples 1 and 2 were subjected to acapability evaluation test. FIG. 1 shows a flow chart of a capabilityevaluation test instrument for a denitration catalyst.

In the test instrument shown in FIG. 1, the denitration catalyst forcleaning a combustion exhaust gas using the honeycomb structure wascharged in a denitration reactor formed of a stainless steel reactiontube, and subjected to a capability evaluation test for an exhaust gashaving an NO concentration of 1,000 ppm under the test condition shownin Table 2 below using methanol as a reducing agent in a concentrationof 1,800 ppm.

TABLE 2 Denitration capability evaluation test condition Gascomposition: NO 1,000 ppmvd Gas composition: air balance Reducing agent:methanol 1,800 ppmvd Water content 5% by volume Space velocity (SV)7,440 Reaction temperature 250° C.

The gas at the outlet port of the denitration reactor was measured forthe concentration of nitrogen oxide (NOx) at the outlet port with an NOxmeter. The denitration rate as the NOx removal capability of thecatalyst was calculated from the measured value with the NOx meteraccording to the following expression (1).

Denitration rate (%)=(NOxin−NOxout)/NOxin×100   (1)

The results of the evaluation test of the denitration catalystcapability thus obtained are shown in Table 4 below.

Evaluation of SOx Durability

In order to confirm that the denitration catalysts for cleaning acombustion exhaust gas using the honeycomb structures obtained inExamples 4 and 5 according to the present invention and ReferenceExamples 1 and 2 were able to decrease effectively a nitrogen oxide evenin the presence of a sulfur oxide (SOx) in a high concentration, thedenitration catalysts were tested for the durability to sulfur trioxideas a sulfur oxide (SOx).

A durability test was performed in such a manner that the denitrationcatalysts for cleaning a combustion exhaust gas using the honeycombstructures obtained in Examples 4 and 5 according to the presentinvention and Reference Examples 1 and 2 were exposed to a gascontaining sulfur oxides (SO₂ and SO₃) for 6 hours under the conditionshown in Table 3 below. The sulfur oxides (SO₂ and SO₃) were sent to theevaporator with a metering pump, and then fed to the reaction tube aftergasification in the evaporator.

TABLE 3 condition of SOx exposure test Gas composition: SO₂ 540 ppmvdGas composition: SO₃ 60 ppmvd Gas composition: air balance Spacevelocity (SV) 7,440 Gas temperature 250° C. Exposure time 6 hours

10

The capability evaluation test corresponding to the cleaning method of acombustion exhaust gas was performed in the same manner as above byusing the denitration catalysts after exposing to sulfur oxides (SO₂ andSO₃). The results of the evaluation test of the denitration catalystcapability thus obtained are shown in Table 4 below.

Evaluation of Strength

For the denitration catalysts for cleaning a combustion exhaust gasusing the honeycomb structures obtained in Examples 4 and 5 according tothe present invention and Reference Examples 1 and 2, the denitrationcatalysts for cleaning a combustion exhaust gas using the honeycombstructures after subjecting to the denitration capability evaluationtest were visually observed, and the results obtained are shown in Table4 below.

Observation of Strength of Denitration Catalyst for Cleaning CombustionExhaust Gas Using Honeycomb Structure

A: The corrugated form of the honeycomb structure after the capabilityevaluation test was normally retained.

B: The corrugated form of the honeycomb structure after the capabilityevaluation test was slightly broken.

TABLE 4 Denitration capability Denitration Denitration Denitration ratebefore rate after SOx capability Evaluation SOx exposure exposureretention of (%) (%) rate (%) strength Example 4 75 73 97.3 A Example 584 68 81.0 A Comparative 85 35 41.2 B Example 1 Comparative 70 40 57.1 BExample 2

As apparent from the results shown in Table 4 described above, accordingto the denitration catalysts using the honeycomb structures of Examples4 and 5 according to the present invention, 80% or more of thedenitration capability before exposing to sulfur oxides (SO₂ and SO₃)was retained even after exposing to sulfur oxides (SO₂ and SO₃), andthus it was confirmed that the denitration catalyst using the honeycombstructure according to the present invention was effective for thesulfur oxide (SOx) durability. It was also confirmed that the additionof a zirconium compound and aluminum oxide was particularly effectivefor enhancing the sulfur oxide (SOx) durability and the catalyststrength.

According to the catalyst for cleaning an exhaust gas using thehoneycomb structure according to the present invention, a nitrogen oxidecan be effectively decreased from a combustion exhaust gas having a highconcentration of a nitrogen oxide (NOx) and a sulfur oxide (SOx) presenttherein, and having a low exhaust gas temperature of 300° C. or less,discharged, for example, from a marine vessel engine, i.e., a largemarine vessel diesel engine, a large scale boiler for a factory, anelectric power plant, a community central heating and air-conditioningplant, and the like.

Example 6

Bismuth nitrate (Bismuth(III) Nitrate Pentahydrate, a trade name,produced by Kishida Chemical Co., Ltd.) was dissolved in ethylene glycol(Ethylene Glycol, a trade name, produced by Kishida Chemical Co., Ltd.),to which FER zeolite having a particle diameter (D50) of 7.0 μm (CP914C,a trade name, produced by Zeolyst International) was added to provide aslurry. The slurry was agitated at 60° C. for 3 hours, and after coolingto room temperature, a zirconia sol (Zircosol AC-20, a trade name,produced by Daiichi Kigenso Kagaku Kogyo Co., Ltd.) as an inorganicbinder was added thereto. 18 g of the catalyst slurry was coated onglass fiber paper cut into 100 mm×150 mm to provide flat slurry-coatedglass paper, and then the flat slurry-coated glass paper was dried at110° C. for 1 hour. Separately, 27.6 g of the slurry described above wascoated on glass paper of 100 mm×230 mm, the slurry-coated glass paperwas shaped with a corrugating mold and a pressing jig, the corrugatedslurry-coated glass paper thus shaped is dried at 110° C. for 1 hour,and released from the mold. Thereafter, the flat slurry-coated glasspaper and the corrugated slurry-coated glass paper were calcined at 500°C. for 3 hours. The flat glass paper and the corrugated glass paper werecombined alternately, thereby producing a honeycomb structure.

Reference Example 3

A denitration catalyst for cleaning a combustion exhaust gas using ahoneycomb structure according to the present invention was produced inthe same manner as in Example 6 provided that the difference fromExample 6 described above was that ion exchanged water was used insteadof ethylene glycol.

Evaluation of Dispersibility

The supported amounts of bismuth on the both surfaces of the flat glassfiber sheets of the honeycomb structures obtained in Example 6 accordingto the present invention and Reference Example 3 were measured with afluorescent X-ray analyzer, and the results obtained are shown in Table5 below.

TABLE 5 Results of measurement of surface bismuth amount (% by weight)Example 6 Reference Example 3 Front surface 5.14 2.70 Back surface 5.484.78

As apparent from the results shown in Table 5 described above, accordingto the denitration catalyst using the honeycomb structure of Example 6according to the present invention, such a substrate of a honeycombstructure is obtained that has the amount of bismuth as the denitrationcatalyst component that is uniformly supported on both the front surfaceand the back surface thereof.

As shown in Table 5 described above, furthermore, it was verified thatthe surface bismuth amount was larger in Example 6 than ReferenceExample 3 on both the front surface and the back surface thereof.

Evaluation of SOx Durability

For the denitration catalysts for cleaning a combustion exhaust gasusing the honeycomb structures of Example 6 according to the presentinvention and Reference Example 3, they were subjected to a denitrationcapability evaluation test under the condition shown in Table 6, andthen tested for the durability to a sulfur oxide (SOx) for 250 hoursunder the condition shown in Table 7. Thereafter, the denitrationcatalysts after exposing to sulfur oxides (SO₂ and SO₃) were againsubjected to a denitration capability evaluation test under thecondition shown in Table 6.

TABLE 6 Condition of denitration capability evaluation test Gascomposition: NO 1,000 ppmvd Gas composition: air balance Water content6% by volume O₂ concentration 14% by volume Reducing agent: methanol1,800 ppmvd Reaction temperature 250° C.

TABLE 7 condition of SOx exposure test Gas composition: NO 1,000 ppmvdGas composition: air balance Water content 6% by volume SO₂concentration 17 ppmvd SO₃ concentration 3 ppmvd O₂ concentration 14% byvolume Reducing agent: methanol 1,800 ppmvd Reaction temperature 250° C.

TABLE 8 Results of measurement of denitration rate Denitration rateDenitration Initial after durability capability denitration rate testretention rate (%) (%) (%) Example 6 74 50 67.6 Reference 74 44 59.5Example 3

The followings are apparent from the results shown in Tables 5 and 8described above. Bismuth nitrate is substantially not dissolved inwater, and thus the ion exchange rate is low. In the case where bismuthis tried to dissolve in an aqueous solution, bismuth that is notion-exchanged is accumulated on the back surface due to the heavy weightrather than zeolite in the preparation of the catalyst, and isincorporated as a catalyst. Accordingly, the denitration catalyst thatis produced by trying to dissolve bismuth in an aqueous solution isliable to be reacted with SOx and has low durability. Accordingly, thesignificant differences are exhibited in the denitration rate after thedurability test and the denitration capability retention rate althoughthe initial denitration rates are equivalent to each other. It wasverified that the use of ethylene glycol as a solvent for dissolvingbismuth as in Example 6 provided excellent durability.

1. A honeycomb structure consisting of a flat inorganic fiber sheetcomprising an inorganic fiber sheet having supported thereon aninorganic binder and zeolite, and a corrugated inorganic fiber sheetcomprising an inorganic fiber sheet having supported thereon the sameinorganic binder and zeolite, which are alternately combined with eachother, wherein it is characterized in that the zeolite has a particlediameter (i.e., a median particle diameter, D50) of from 0.5 to 10.0 μm.2. The honeycomb structure according to claim 1, wherein it ischaracterized in that the inorganic fiber sheet is a glass fiber sheet.3. A catalyst for cleaning an exhaust gas using a honeycomb structure,wherein it is characterized in that it comprises a denitration catalystcomponent that is supported on the zeolite of the honeycomb structureaccording to claim
 1. 4. The catalyst for cleaning an exhaust gas usinga honeycomb structure according to claim 3, wherein it is characterizedin that the inorganic binder is formed of zirconia or alumina.
 5. Thecatalyst for cleaning an exhaust gas using a honeycomb structureaccording to claim 3, wherein the denitration catalyst component isbismuth.
 6. A method for producing the catalyst for cleaning an exhaustgas according to claim 5, comprising a step of supporting bismuth (Bi)on the zeolite, in the step, bismuth (Bi) being dissolved in a solvent,the solvent used being a compound having one or more alkoxy group andone or more hydroxy group per molecule, a compound having two or morehydroxy groups per molecule, or an acid.
 7. A method for producing acatalyst for cleaning an exhaust gas comprising an inorganic fiber sheethaving supported thereon an inorganic binder and zeolite, comprising astep of supporting bismuth (Bi) as a denitration catalyst component onthe zeolite, in the step, bismuth (Bi) being dissolved in a solvent, thesolvent used being a compound having one or more alkoxy group and one ormore hydroxy group per molecule, a compound having two or more hydroxygroups per molecule, or an acid.
 8. A catalyst for cleaning an exhaustgas using a honeycomb structure, wherein it is characterized in that itcomprises a denitration catalyst component that is supported on thezeolite of the honeycomb structure according to claim
 2. 9. The catalystfor cleaning an exhaust gas using a honeycomb structure according toclaim 8, wherein it is characterized in that the inorganic binder isformed of zirconia or alumina.
 10. The catalyst for cleaning an exhaustgas using a honeycomb structure according to claim 8, wherein thedenitration catalyst component is bismuth.
 11. A method for producingthe catalyst for cleaning an exhaust gas according to claim 10,comprising a step of supporting bismuth (Bi) on the zeolite, in thestep, bismuth (Bi) being dissolved in a solvent, the solvent used beinga compound having one or more alkoxy group and one or more hydroxy groupper molecule, a compound having two or more hydroxy groups per molecule,or an acid.